The present invention relates to a semiconductor integrated circuit and a method for controlling the semiconductor integrated circuit.
FIG. 1 shows an exemplary block diagram of a semiconductor integrated circuit that uses power supply voltages from plural power supplies. The semiconductor integrated circuit 101 includes domains 102, 103, an asynchronous bridge section 104, and a power supply control section 105. The domain 102 is a circuit section that uses the power supply voltage from a DC/DC power supply 111. The domain 103 is a circuit section that uses the power supply from the DC/DC power supply 112. The power supply section 105 controls the power supply voltage that the DC/DC power supplies 111, 112 output. If the domains 102 and 103 use different power supply voltages and a signal is transmitted and received between the domains 102 and 103, the voltage level of the signal is converted and transmitted by the asynchronous bridge section 104. The asynchronous bridge section 104 may change the timing of the signal.
FIG. 2 shows an exemplary block diagram of a semiconductor integrated circuit that is not provided with the asynchronous bridge section 104. In FIG. 2, like numerals depict like elements as those shown in FIG. 1. As shown in FIG. 2, the domains 102 and 103 are directly connected in the semiconductor integrated circuit 101A.
Japanese Patent Application Laid-Open No. H 9-218849 discloses a method and a device to bridge devices that operate at different clock frequencies.
For example, the power supplies 111, 112 shown in FIG. 1 are DC/DC power supplies, and the output voltage of each of the power supplies 111, 112 is a 1.2V power supply voltage. For example, when the operation clock of the circuits in the domains is drastically changed, a rapid current fluctuation occurs, as shown in FIG. 3. As a result, when the power supply voltage is affected by the rapid change of load current, a phenomenon can occur that is characterized by a change in the power supply voltage, such as a change between 1.1V and 1.3V, for example. FIG. 3 is a timing chart that shows the effect of load change on the power supply voltage. As shown in FIG. 3, Vout is the output power supply voltage of the DC/DC power supply, and IL is the current in the DC/DC power supply, wherein the current IL changes, for example, from 100 mA to 600 mA, as affected by the load change.
If such a phenomenon occurs in the DC/DC power supply that includes the power supplies 111, 112, an excessive potential difference of 0.2V or more can result between the domains 102 and 103. As a result, for example, if the semiconductor integrated circuit 101 is required to process a heavy load through domains 102 and 103, which operate at the same high power supply voltage, and the signal is transmitted and received between the domains 102 and 103 through the asynchronous bridge section 104 for the aforementioned reason, high-speed data may not be transferred.